Measurement of LASIK flap thickness with anterior segment optical coherence tomography

To assess the interobserver variability and agreement of anterior segment optical coherence tomography (OCT) in the measurement of LASIK flap thickness, and to compare the results with intraoperative ultrasound pachymetry measurements.

Thirty-nine eyes of 20 consecutive patients undergoing LASIK with the XP microkeratome (Bausch & Lomb) and ALLEGRETTO Eye-Q laser system (WaveLight Inc) had corneal flap thickness measured with SP-100 ultrasound (Tomey Corp) intraoperatively and with OCT (Visante; Carl Zeiss Meditec Inc) postoperatively. Interobserver assessment was performed by comparing the flap thickness measurements obtained from the same scan by 2 masked, independent observers. Agreement of OCT scan was determined by assessment of 2 different scans of the same eye by the same observer.

Mean (+/- standard deviation) flap thickness measured by ultrasound, OCT scan 1 (OCT 1-1) and scan 2 (OCT 1-2) assessed by observer 1, and OCT scan 1 (OCT 2-1) and scan 2 (OCT 2-2) assessed by observer 2 were 112.79+/-19.71, 124.69+/-17.02, 127.59+/-17.32, 130.59+/-20.34, and 133.74+/-19.70 microm, respectively. No statistically significant difference among the interobserver measurements was seen. The difference between OCT and ultrasound measurements by observers 1 and 2 was statistically significant (P<.01). Correlation among all measurements was statistically significant. Good agreement among the OCT scans was noted.

Optical coherence tomography showed good correlation among measurements and observers for different OCT measurements in the assessment of corneal flap thickness after LASIK. However, OCT significantly overestimated flap thickness when compared to ultrasound despite a good correlation between these two modalities. Optical coherence tomography measurements should not be substituted for standad ultrasound measurements at the present time.